13.       
　　In an attempt to sell radio advertising¹ time, this ad claims that radio advertising will make businesses more profitable. The evidence cited is a ten percent increase in business that the Cumquat Cafe has experienced in the year during which it advertised on the local radio station. This argument is unconvincing because two questionable² assumptions must be made for the stated evidence to support the authors conclusion.

      The first assumption is that radio advertising alone has caused the increase in business at the Cumquat Cafe. This assumption is questionable because it overlooks a number of other factors that might have contributed to the Cumquat's success. For example, the Cumquat might have changed owners or chefs; it might have launched a coupon³ ad campaign in the local print media; or it might have changed or updated the menu. Yet another possibility is that a local competitor went out of business. These are just a few of the factors that could help explain the Cumquat's growth. Because the author fails to eliminate these possibilities, the assumption in question need not be accepted.

      Even if it is granted that radio advertising is responsible for the Cumquat's success, another assumption must be made before we can conclude that radio advertising will result in increased profits for businesses in general. We must also assume that what is true of the Cumquat will likewise be true of most other businesses. But there are all kinds of important differences between cafes and other businesses that could affect how radio audiences react to their advertising. We cannot safely assume that because a small restaurant has benefited from radio advertising, that any and all local businesses will similarly benefit.

      In conclusion, it would be imprudent for a business to invest in radio advertising solely⁴ on the basis of the evidence presented. To strengthen the conclusion, it must be established that radio advertising was the principal cause of increased business at the Cumquat. Once this is shown, it must be determined⁵ that the business in question is sufficiently⁶ like the Cumquat, and so can expect similar returns from investment in radio ad time.

14.   
　　 Two years ago Nova High School began to use interactive⁷ computer instruction in three academic subjects. The school dropout⁸ rate declined immediately and last year's graduates have reported some impressive achievements in college. In future budgets the school board should use a greater portion of the available funds to buy more computers, and the schools in the district should adopt interactive computer instruction throughout the curriculum.
 
Sample Essay 1:
      The argument that the school board should buy more computers and adopt interactive computer instruction is not entirely⁹ logically convincing, since it ignores certain crucial assumptions.

      First, the argument assumes that the decline of school dropout and the achievements of last year's graduates' results from the adoption¹⁰ of interactive computer instruction. However, there are several reasons why this might not be true. For example, achievements could have been made in other subjects than the ones with interactive computer instruction. Or last years' graduates might not have been given the interactive computer instruction. Or the decline of the rate of dropout could be attributed to stricter discipline applied¹¹ last year.

       Second, even supposing the Nova High School's decline of the dropout and last year's graduates' achievements benefit directly from the usage of interactive computer instruction, the success of the instruction in one school may not ensure thesuccess in other schools. If it does not suit other schools, the instruction will not work.

       Finally, even if the decline of the rate of dropout and the achievements of the last year's graduates' are the direct results of the interactive computer instruction, we still do not know whether the school can afford to apply the instructionon all the subjects or to all the students. If the school does not have sufficient fund and has to cut budgets on other projects such as the library, the quality of the school's education will also compromise.   
    
      Thus, the argument is not completely sound. The evidence in support of the conclusion that the dropout rate declined and last year's graduates made impressive achievements does little to prove the conclusion-that other schools should use a greater portion of their funds to apply the instruction-since it does not address the assumptions I have already raised. Ultimately, the argument might have been strengthened by making it clear that the decline of the dropout rate and the achievements of the graduates are the direct results of interactive computer instruction, that the instruction is also applicable to other schools in the district, and that the instruction is affordable¹² to all the schools in the district.
 
Sample Essay 2:
      The editorial recommends that the school board of Nova High spend a greater portion of available funds on the purchase of additional computers and adopt interactive computer instruction throughout the curriculum. Two reasons are offered in support of this recommendation. First, the introduction of interactive computer instruction in three academic subjects was immediately followed by a decline in the school dropout rate. Second, last year's graduates experienced impressive achievements in college. This argument is unconvincing for two reasons.

      To begin with, this argument is a classic instance of "after this, therefore because of this" reasoning. The mere¹³ fact that the introduction of interactive computer instruction preceded the impressive performance of recent graduates and the decline in the dropout rate is insufficient¹⁴ to conclude that it was the cause of these events. Many other factors could bring about these same results. For example, the school may have implemented¹⁵ counseling and training programs that bettermeet the needs of students who might otherwise leave school to take jobs. In addition, the school may have introduced programs to better prepare students for college.

      Secondly¹⁶, the author assumes that the impressive achievements of last year's graduates bear some relation to the introduction of interactive computer instruction at Nova High. However, no evidence is offered to support this assumption. Lacking evidence that links the achievements of the recent graduates to the interactive instruction, it is presumptuous¹⁷ to suggest that the computer instruction was in some way responsible for the students' impressive performance.

      In conclusion, the recommendation that Nova High spend a greater portion of available funds on the purchase of additional computers and adopt interactive computer instruction throughout the curriculum is ill-founded. To strengthen this recommendation the author would have to demonstrate that the decline in the dropout rate and the impressive performance of recent graduates came about as a result of the use of computer-interactive instruction. All that has been shown so far is a correlation¹⁸ between these events.